these files and folders contain logging information for applications and services running on your system. The Operating System (OS) has become pretty good at automatically managing these logs in a process that is known as "rotating".
These services and logs are a great way in monitoring the health of your system and protecting it. Not only that, but the logs for services such as a web server contain information about every single request - allowing developers or administrators to diagnose performance issues or investigate an intruder's activity. For example, the two types of log files below that are of interest: